Over the past few years the supply of high quality crude oils has diminished and the price of easily refined oils substantially increased. Frequently suppliers of high quality crudes require purchase of great volumes of less desirable crudes, such as those containing metal or organo-metallic contaminants, or heavier gravity crude oils. Further, treatment of crude oils manufactured as "synthetic" crudes from shale, coal, tar sands or other low gravity oils, require decontamination of the heavier and/or metal components and inert materials to produce a crude that can be easily processed in conventional hydroprocessing units available for refining high quality crudes. For example, among the synthetic crudes and tars, a common characteristic is their high end boiling points, high viscosity and high metals nitrogen and sulfur content. Some heavy petroleum crudes also contain nickel, vanadium and iron in sufficient quantities to foul and contaminate all downstream refining processes. While various arrangements for reacting such low quality crudes have been proposed including demetalization, desulfurization, hydrocracking, hydrogenating, and dehydrogenating, such processes have been basically conducted in fixed bed catalytic reactors. Such reactors require frequent regeneration to maintain the activity of the catalyst. An example of such a system for treating relatively low metal content crudes is shown in U.S. Pat. No. 3,826,737 Pegels, et al., issued July 30, 1974. The demetallation reactor disclosed is stated to be suitable for countercurrent or cocurrent flow of the catalyst and feed, although the patent is directed primarily to cocurrent operation. A system disclosing countercurrent operation is shown in U.S. Pat. No. 3,882,015, Carson, issued May 6, 1975. This patent discloses a unitary multistage reactor for countercurrently reacting a fluid stream with catalyst particles. However, the system is primarily for reactions involving light naphtha hydrocarbons rather than crude oils.
Reaction schemes and catalysts proposed for catalytic upgrading processes by demetallizing, desulferizing, hydrocracking, hydrogenating, or denitrogenating, typically involve treating residual oils that have contaminant levels relatively much lower than those of the heavy and synthetic crudes or tars discussed above. U.S. Pat. No. 3,826,737, Pegels et al., issued July 30, 1974, discloses a continuous process and apparatus for catalytically treating residual oils. The process is disclosed as operating on a feed having a total metals content of less than 65 ppm by weight. The demetallation reactor disclosed is stated to be suitable either for countercurrent or cocurrent operation, although the patent is directed primarily to cocurrent operation. U.S. Pat. No. 3,882,015, Carson, issued May 6, 1975, discloses a unitary multiple-stage reaction system for countercurrently contacting a fluid reactant stream with catalyst particles, primarily for reactions involving light naphtha hydrocarbons.
As noted above, most process schemes relating to desulfurizing and demetallizing heavily contaminated feedstocks, if they do not relate to fixed bed operation, relate to cocurrent moving bed operation. In such operation the feed and the catalyst both flow through the reactor in the same direction. Examples of these schemes include: U.S. Pat. No. 3,730,880, Van der Toorn, et al., issued May 1, 1973--residual oil desulfurization in a cocurrent intermittent moving bed; U.S. Pat. No. 3,880,598, Van der Toorn, et al., issued Apr. 29, 1975--residual oil hydrodesulfurization in an intermittent cocurrent moving bed operation; U.S. Pat. No. 4,312,741 Jacquin, issued Jan. 26, 1982--conversion of hydrocarbons or bituminous shale in the liquid phase in semi-stationary or ebullating beds with intermittent countercurrent catalyst flow.
Fixed bed and cocurrent moving beds are easier to design than countercurrent moving beds. The ease of operation of cocurrent as opposed to countercurrent moving beds is discussed in the literature, which discloses a large number of reaction schemes, apparatus, and processes for adding and removing catalysts and reactants in these processes. Some examples of these disclosures include: U.S. Pat. No. 2,956,010, Buckner, issued Oct. 11, 1960--method and apparatus for the supply of reactant and contact material to moving masses of granular contact materials; U.S. Pat. No. 3,336,217, Meaux, issued Aug. 15, 1967--method and apparatus for intermittently withdrawing particulate catalysts from the bed of a high pressure and temperature reactor; U.S. Pat. No. 3,547,809, Ehrlich, et al., issued Dec. 15, 1970--a process for the addition and withdrawal of solids from a high pressure reaction vessel by using a pressurized liquid transfer medium; U.S. Pat. No. 3,785,963, Boyd, et al., issued Jan. 15, 1974--withdrawing uniform amounts of solids from a movable bed of solids by a system comprising a plurality of conduits equally spaced across the solids cross-sectional area; U.S Pat. No. 3,849,295, Addison, issued Nov. 19, 1974--removal of catalysts from moving bed reactor systems having poor catalyst flow due to liquid reactants or catalyst agglomeration problems; U.S. Pat. No. 3,856,662, Greenwood, issued Dec. 24, 1974--solids withdrawal and transport vessels and methods for use in superatmospheric pressure systems; U.S. Pat. No. 4,188,283, Czajkowski, et al., issued Feb. 12, 1980--start up method for moving bed reactors used in hydrogenating olefin-containing hydrocarbons.
U.S. Pat. No. 3,910,834, Anderson, issued Oct. 7, 1975, discloses a process in which a solids-containing feed, derived from oil shale or tar sands, is passed countercurrently or cocurrently through a moving bed reactor in a dual function system which simultaneously filters out the solids and hydroprocesses the feed. Catalyst is moved through the reactor by maintaining a desired pressure drop in the catalyst bed and a desired solids filtraton rate. Countercurrent flow of the synthetic, solids-containing feed and the catalyst is disclosed as a preferred mode of operation. The patent teaches that countercurrent flow prevents escape of filtered particulate matter when the catalyst bed moves.
Other reaction schemes for demetallation processes include the use of ebullating or fluidized beds. In an ebullating bed, a liquid or gaseous material flows upwardly through a vessel containing a mass of solid particles. The solid particle mass is maintained in random motion by the upflowing streams and the physical space occupied by the catalyst bed is larger ("expanded") as compared either to the space occupied by the catalyst bed when no material flows through it or to a fixed- or a moving bed-type reaction zone. Discussions of ebullating bed reaction zones and their characteristics can be found in Re. No. 25,770 of U.S. Pat. No. 2,987,465, Johanson, issued June 6, 1961, as well as in U.S. Pat. No. 3,901,792, Wolk, et al., issued Aug. 26, 1975--demetallizing and desulferizing crude or atmospheric residual oils using an ebullating bed, and, in U.S. Pat. No. 4,217,206, Nongbri, issued Aug. 12, 1980 catalytically demetallizing Venezuelian crude oils using fixed and preferably ebullating beds.
The non-patent literature also discusses upgrading heavy, contaminated oils. For example, LC-Fining, as described in "Hydrocarbon Processing", pg. 107, May 1979, involves the use of an ebullating bed reactor. The ebullating or expanded bed design is disclosed as allowing very heavy feedstocks to be processed without shutting down the unit for catalyst replacement. The H-OIL Process as described in "Hydrocarbon Processing", pg. 112, September 1980, uses an ebullating bed with onstream catalyst addition and withdrawal to upgrade high metals and high sulfur content feeds. The Shell-Bunker Flow Process as described in the Oil and Gas Journal, pg. 120, Dec. 1, 1980, involves an intermittent cocurrent flow as described in the Pegels and Van der Toorn patents discussed above.
Although countercurrent moving beds are known to be useful for demetallation and desulfurization reactions, the problems of countercurrent flow of catalyst to the liquid and gas, particularly hydrogen, as opposed to cocurrent or even fixed bed operation have not been solved so that practical operation was possible. By employing the process of the present invention, such a countercurrent slowly moving bed of catalyst may be utilized with improved contact of gas and liquid and at the same time progressive improvement in the contact quality of both the fresh or regenerated catalyst with the lighter components is achieved. Further, a greater portion of contaminants are removed with the spent catalyst.
In downflow reactors, if the liquid feed contains solids, the solids tend to pack and form obstructions. The problem is further aggravated if the feed stream is comprised of gases as well as solids and liquids. Accordingly, upflow reactors are commonly employed in coal liquefaction systems such as the liquefaction process disclosed in U.S. Pat. No. 4,083,769, Hildebrand, et al., issued Apr. 8, 1978. As there taught, hydrogen, ground coal and solvent are preheated and passed to a dissolver wherein the coal is substantially dissolved at a temperature in the range 750.degree.-900.degree. F. (379.degree.-482.degree. C.) and at a pressure in the range 3100-5000 psi (217 kg/cm.sup.2 -350 kg/cm.sup.2). The dissolver is an empty upflow reactor vessel which provides sufficient residence time for the dissolution of the ground coal particled to occur. Solvent, dissolved coal, coal residue and hydrogen from the dissolver are then passed to an upflow catalytic hydrogenation reactor operating at a lower temperature, say 25.degree.-150.degree. F. (13.9.degree.-83.3.degree. C.), than the dissolver.
Since the hydrogen is mixed with the coal slurry prior to the preheating step to avoid coking in the heater, little or no control is exerted over the degree of liquid and gas mixing which occurs in the dissolver or catalytic reactor. With multiphase flow, gas channeling and/or slugging in these units may occur. The presence of either condition is undesirable since both result in inadequate contacting of the reactants and the slugging may also create damaging equipment vibrations. If channeling results from inadequate mixing of the gas, especially hydrogen, coking of either catalyst or reactant, or both, and equipment fouling can result. Such channeling or slugging may be further amplified by downward movement of the catalyst bed, induced by funneling and removal of catalyst from the bed.
Thus, it is apparent that a need exists for a feed distributor which will accept streams comprising liquids, gases and solids and evenly distribute the phases without plugging or producing undue erosion during continuous countercurrent movement of both feed and catalyst.
Mixed phase distributors are known in the art, such as those disclosed in U.S. Pat. Nos. 3,524,731; 4,111,663; 3,146,189; 3,195,987 and 4,187,169, for fixed beds. Copending application Ser. No. 278,789, filed June 29, 1981, assigned to the assignee of the present application, also discloses an upflow feed stream having a distribution system arranged to feed liquids, solids, and gases through a relatively fixed bed of catalyst. It does not disclose a method of removing catalyst from the vessel or use of the distributor as a support bin for a moving catalyst bed and to aid removal of catalyst particles from the bed.